Recovery of lead values from solution

ABSTRACT

Recovery of lead values from lead-bearing material, by leaching the said material at ambient temperature for a period not exceeding 1 hour with a mixture of ammonium sulfate and aqueous ammonia to produce a supersaturated solution, separating undissolved substances, treating the resultant solution at a temperature higher than that at which the leaching operation was effected without substantial loss of ammonia, to cause precipitation of a major portion of the lead content from the said solution, and separating the precipitated solids.

United States Patent [72] inventors Geoffrey Charles Bratt Tasmania,Australia; Dereck Wilson Brown, Singapore, Singapore [21] Appl. No.843,295 [22] Filed July 22, 1969 [45] Patented Nov. 16, 1971 [73]Assignee Electrolytic Zinc Company of Australia Limited Melbourne,Victoria, Australia [32] Priority July 25, 1968 [3 3] Australia [3 1 41175/68 [54] RECOVERY OF LEAD VALUES FROM SOLUTION 2 Claims, 1 DrawingFig. [52] U.S.Cl 23/127, 23/119, 23/301, 23/303, 23/312 [51] 1nt.Cl C0lg21/20 [50] Field of Search 23/127, 117, 301, 305, 312,1l9;204/119 [56]References Cited UNITED STATES PATENTS 3,440,155 4/1969 Pickering et al.204/1 19 OTHER REFERENCES McPherson & Henderson Book, A Course inGeneral Chemistry, Third Ed., Revised (1927), page 211, Ginn & Co., NewYork.

Hackh s Chemical Dictionary, by Julius Grant, Third Ed., Revised, 1944,page 823, McGraw-Hill Book Company, New York.

Primary Examiner-Edward Stem An0rneyPierce, Scheffler & Parker TotalSulphate Welght /o.

Simplified representation of equilibrium PAiENiEurmv 16 lSTl TotalSulphate Weight /o.

e. 29; E E2.

Simplified representation of equilibrium solubilities of lead sulphatein ammoniacal ammonium sulphate solutions at 25C.

Ivrvvswrons owl lawsuits,

Aiiorne RECOVERY OF LEAD VALUES FROM SOLUTION This invention relates toa process for the dissolution of lead values from lead-bearing material,as hereinafter specified, by an aqueous ammoniacal ammonium sulfatesolution, and the recovery of lead values from the aforementionedsolution.

Materials which may be treated in accordance with this invention includeores, concentrates, residues, calcines, drosses, slags, dusts or fumeswhich contain lead. It will be understood that the lead must be presentas oxide, sulfate or basic sulfate or converted to one of thesecompounds by suitable pretreatment.

In this specification and in the appended claims, the followingabbreviations are used:

g. grams g./l. grams per liter ml. milliliters S.G. =specific gravitywt. weight hr. hour T/Pb total lead T/NH total ammonia T/SO totalsulfate In our US. Pat. No. 3,440,155 we have described and claimed aprocess for the extraction of lead values from such materials. Thisprocess includes pretreatment by suitable techniques to ensure theconversion of the lead in the starting material to the oxide, hydroxide,sulfate or basic sulphate, the dissolution of these lead compounds in anaqueous ammoniacal ammonium sulfate solution of selected composition,and the subsequent recovery of lead or lead compounds by a number oftechniques.

One method which may be employed for the recovery of lead compounds fromthe pregnant'liquors is by distilling ammonia from such solutions. Thismethod permits the precipitation of lead ammonium sulfate monobasic leadsulfate or mixtures of these two compounds. By adjusting the solutioncomposition, either by selection of the components added during leachingor by additions during or immediately prior to distillation, so that thetotal sulfate concentration is in the range 190 g./l. to 360 g./l. andthe total ammonia concentration is in the range 80 g./l. to 240 g./l.,the product from the distillation will be substantially all leadammonium sulfate Such a procedure is useful in many process applicationsespecially when waste heat is available from other operations.

It has now been found that by careful selection of the amounts ofammonium sulfate ammonia and water added to the material during leachingand by avoiding unnecessarily long leaching times, a lead-bearingsolution is produced which is termed supersaturated, as-hereinafterdefined. Further-it has been found that such supersaturated solutionsare substantially stable at the leaching temperature in the range l5-35C. but which on warming for short periods to temperatures above 45 C.,e.g., at a temperature in the range 4565C. for from 0.5 to 2.0 hours,especially in the presence of seed crystals, become unstable andprecipitate a major part of the dissolved lead. It has been furtherfound that by suitable selection of the sulfate level obtained in theleach liquor, the lead compound precipitated is substantially leadammonium sulfate When a lead compound such as lead sulfate or a materialcontaining lead sulfate is agitated with a mixture of ammoni um sulfateand aqueous ammonia for a prolonged period of time, lead-bearingsolution is produced which, after removal of undissolved substances, maybe stored for an indefinite time without precipitation of leadcompounds. Such solutions are considered to be saturated or equilibriumsolutions. The composition of these equilibrium solutions mayconveniently be defined by a diagram such as the accompanying FIG.

We have also found that if the period of agitation does not exceed 1hour and the solution composition is properly selected it is possible todissolve more lead than if agitation is tontinued until the equilibriumconcentration is reached. After removal of undissolved substances and onprolonged standing or warming such solutions will deposit lead compoundsuntil the solution achieves the equilibrium composition. Solutionshaving these characteristics are herein termed supersaturated solutions.

According to the present invention there is provided a process for therecovery of lead values from lead-bearing material, as hereinbeforedefined, which includes leaching at ambient temperature, for a periodnot exceeding l hour, with a mixture of ammonium sulfate and aqueousammonia to produce a supersaturated solution, as hereinbefore defined,separating undissolved substances, treating the resulting solution at atemperature higher than the leaching operation and without substantialloss of ammonia to cause precipitation of a major part of the leadtherein, and separating the precipitated solids and liquor. Afterseparation of the precipitated solids, the liquor may be recycled to theleaching stage.

In one form of the invention there is provided a process for therecovery of lead values from lead-bearing materials, which includes theleaching of the material with a mixture of ammonium sulfate and aqueousammonia for a period of between I and 60 minutes to produce a solutionwhich is supersaturated and having a composition in the range total leadID to I40 g./l., total ammonia I25 to 225 g./l., total sulfate 200 to370 g./l., separating the undissolved substances, heating the solutionsto and maintaining them at a temperature in the range 40 to 60 C. in thepresence of0.l to 40 g./l. of crystals of either lead ammonium sulfateor monobasic lead sulfate so as to precipitate a major portion of thelead as a mixture containing varying proportions of lead ammoniumsulfate and monobasic lead sulfate The precipitation is preferablycarried out under conditions which minimize ammonia loss.

In a preferred embodiment of the invention there is provided a processfor the recovery of lead values from lead-bearing materials, whichincludes the leaching of the material with a mixture of ammonium sulfateand aqueous ammonia for a period of between I and 15 minutes, to producea solution which is supersaturated and having a composition the rangetotal lead 60 to g./l., total ammonia to I80 g./l., total sulfate 270 to320 g./l., separating the undissolved substances, heating the saidsolution to and maintaining it at a temperature in the range 45 to 60 C.in a vessel designed to minimize loss of ammonia gas and in the presenceof 0.1 to 2.0 g./l. of crystals of lead ammonium sulfate for a period ofbetween 0.5 and 2 hours so as to precipitate more than 50 percent of thelead contained therein as substantially pure lead ammonium sulphate. Theprecipitated lead compounds are substantially free from impurities suchas copper and zinc which may be present in the solution.

After filtration to remove the lead compounds, the solution may betreated by a variety of methods to remove accumulated impurities. Aftercooling to l5 to 30 C. the solution is suitable for recycling to theleaching or solution preparation stage ofa cyclic process.

To obtain a supersaturated solution composition in the desired range,the amounts of lead-bearing material. recycled solution, fresh aqueousammonia (to allow for losses due to spillage, evaporation, etc.)ammonium sulfate (either fresh or recycled from the decomposition oflead ammonium sulfate) "may be blended in the required proportions. Thevolatilization of ammonia from the supersaturated solution increases asthe temperature increases and hence to substantially avoid losses due tosuch volatilization the various operations are preferably conducted inclosed vessels.

That precipitated lead material which is substantially pUl'L' leadammonium sulfate may suitably be treated to recover the lead values inthe form of lead sulfate, and to provide ammoni urn sulfate suitable forrecycling to the leaching Stage lhl may be effected by repulping thelead precipitate with water or with an aqueous ammonium sulfate solutioncontaining up to about 21 percent by weight of ammonium sulfate (at theconclusion of the decomposition) at an elevated temperature (in therange 50 to I00 C.). The lead ammonium sulfate is thereby decomposedinto its component salts, and the insolu ble lead sulfate may beseparated by conventional techniques and the ammonium sulfate solutionrecycled Alternatively, the lead ammonium sulfate may be treated torecover the lead values in the form of lead sulphate, and to providegaseous ammonia and sulfur trixoide for recycling to the leaching stage.This may be effected by heating the lead ammonium sulfate to atemperature in the range 380 to 450 C. The lead sulfate is then in theform suitable for reduction to metallic lead by conventionalpyrometallurgical methods and the gases containing ammonia and oxides ofsulfur may be treated by water scrubbing operations to yield ammoniumsulfate, which may be recycled.

That precipitated lead material which is substantially pure monobasiclead sulfate may be treated directly by conventional pyrometallurgicalreduction methods to produce metallic lead or it may be given a priortreatment with concentrated ammonium sulfate solutions at an elevatedtemperature (in the range 50 to 100 C.) to form lead sulfate andregenerate gaseous ammonia.

Mixtures of lead ammonium sulfate and monobasic lead sulfate may betreated by a combination of the above methods according to theircomposition.

The present process possesses a number of inherent ad vantages comparedwith previously disclosed processes. Thus the crystallization of leadammonium sulfate at low temperatures avoids the costs and processcomplications associated with the precipitation by steam distillationoperations. The recovery of lead finally as lead sulfate. afterdecomposition of the lead ammonium sulfate. or conversion of monobasiclead sulfate to lead sulphate, means that if the material fed to theleaching step is, or contains. lead sulfate, then a ready control of thesulfate balance of the system is possible. This process also recoversthe lead values from solution in a form that is readily amenable tofurther treatment for the recovery of metallic lead.

From the previous description it will be understood that this processmay be readily operated either as a batch or as a con tinuous operation.

The invention is illustrated by the following examples EXAMPLE I Asolution (solution A) of composition Pb 70 s 1 1| TIN "1 I65 8 it T/SO.ziis g II was prepared by agitation together for IS minutes at 25 of thefollowing materials.

PbSO, 24 g 0.880 aqueous ammonia 74 ml NH. ,SO 86 g Water lllll mlComplete dissolution of the solids occurred Portion of this solution Awas set aside and maintained at 2 After 24 hours no crystallization oflead compounds had occurred Another portion of solution A of volume 194ml was heated to 50 C and maintained at this temperature for 3 hours ina closed vessel. Crystallization of lead ammonium sulfate oc curred. Thewashed and dried crystals contained 9 g. of lead as lead ammoniumsulfatev That is. 65 percent of the lead in solu tion A had beenrecovered by crystallization After filtration to recover the crystals.the filtrate (solution B) was used to leach a further l0 g. ofleadsulfate at 25C An addition of 4 g of ammonium sulfate was made to theleach solution to bring the solution into the desired range l lnpractice this ammonium sulfate would be supplied from material recoveredby the descomposition of lead ammonium sulphate).

The resulting liquor (solution C) was seeded with 0 l g. of the wetcrystals obtained from solution A and heated and maintained at 50 C. forminutes. Crystallization occurred and lead ammonium sulfate containing6.6 g. of lead was removed by filtration That is. 66 percent of the leadin solution C was recovered as lead ammonium sulfate EXAMPLE 2 Asolution (solution D) was produced by agitation together for IS minutesat 25 C ofthe following components:

l87.6 g process residue containing 7.6% Pb as Pl'iSO 86 g. ammoniumsulfate 74 ml. 0.880 aqueous ammonia I08 ml. water followed byfiltration to remove the insoluble materials. The composition ofsolution D was Pb 13 s g./l. TINH, in g./l. T150. 293 g./l.

Comparison of the composition of solution D with saturated solutions ofthe same total ammonia and total sulfate depicted in the drawing showsthat solution D contains about 24 g./l. lead in excess of the saturationvalue and hence is a supersaturated solution One hundred ml of solutionD was warmed to and maintained to 50 l'or 0m: hour in the presence ofOil g. of previously prepared crystals oflead ammonium sulfate Afterfiltration and washing the precipitate, the filtrate and washings (88ml.) (solution F.) were analyzed and shown to contain only 48 4 g./l.lead That is, 43.l percent of the lead has been recovered from thesolution as lead ammonium sulfate.

EXAMPLE 3 The effect of time. temperature and amount of seed crystals onthe crystallization of lead ammonium sulfate is illustrated by the datatabulated below obtained using 120 ml. portions of the solution.prepared in the same manner as solution A of example l. and seedcrystals oflead ammonium sulfate ilead precipitated as lead ammoniumsulfate excluding amount added as seed crystals EXAMPLE 4 Four hundredand thirty six grams of a residue (Fl containing II 1 percent total leadpercent soluble in H) percent neutral ammonium acetate at the boilingpoint) was agitated for l minutes with a mixture ot ammonium sulfatecrystals 220 g. aqueous ammonia 201 mls (S.G. =().89l) and water 263 g.The solution obtained (solution G) after the removal of insolubleresidue had a composition Ph 63.4 .11. TINH, r04 "H50. 290 g ll and hada volume of380 ml.

Three hundred and sixty five milliliter of solution G was warmed to 60C. in the presence of 0.1 g. of lead ammonium sulfate crystals, andmaintained at this temperature for 1 hr., then filtered. The productsfrom filtration were a solution H and solids l which had the compositionindicated below:

Solution H Solids l (sparingly washed,

1.8 displacements) Pb 27.3 gJl. Pb 475% T/SO, 292 g./l. T/SO, 43.5%

Wt. (washed and dried) 34.72 g.

The theoretical composition of lead ammonium sulfate is lead 47.6percent, total ammonia 7.85 percent, total sulfate 44.] percent.

Thus in the primary leach 99 percent of the lead soluble in percentneutral ammonium acetate at the boiling point was dissolved, and duringthe precipitation stage 57 percent of the lead contained in the solutionwas precipitated as lead ammonium sulfate.

Portion of solution H was adjusted in composition by additions ofaqueous ammonia (to compensate for losses during handling) and ammoniumsulfate (to compensate for removal as lead ammonium sulfate and thenused to leach a further portion of residue F. The resulting solution wastreated in the same way as solution G. This procedure was repeated fivetimes, the lead extraction during each stage of leaching being greaterthan 97 percent and the yield of lead compounds dur ing theprecipitation stages were 71, 71, 76, 73, and 72 respec' tively. Theliquor after the final precipitation stage was analyzed for impuritieswhich had been derived from residue F and shown to contain Zn 2.75 g.ll.Cu 0.42 g./l. CaO 0.03 g./|. MgO 0.03 .11. Cd 0.004 g./l.

The solids precipitated during the final stage were also analyzed forimpurities in a sparingly washed state (1.8 displacement wash withlead-free aqueous ammonium sulfate solution) and after extensive waterwashing. The results obtained are tabulated below:

Precipitated Solids Analysis Sparingly washed Thoroughly washed 1. Aprocess for the recovery of lead values from a material containing aleast one compound selected from the group consisting of lead oxide,lead sulfate and basic lead sulfate which comprises leaching the saidmaterial at a temperature in the range 15 to l5 C. and for a period notexceeding 1 hour with a mixture of ammonium sulfate and aqueous ammoniato produce a supersaturated solution having a composition within therange total sulfate 200 to 370 g./l., total ammonia to 225 g./l. andtotal lead 10 to g./l., separating undissolved substances, treating theresulting solution at a temperature in the range 45 to 65 C., in thepresence of0.l40.0 g./l. of seed crystals of a salt selected from thegroup consisting of lead ammonium sulfate and basic lead sulfate, for aperiod of between 0.5 hour and 2.0 hours without substantial loss ofammonia to cause precipitation of a majorportion of the lead therein asa member of the group consisting of lead ammonium sulfate, monobasiclead sulfate, and mixtures of these two compounds, and separating theprecipitated solids and liquor.

2. A process for the recovery of lead values from a material containingat least one compound selected from the group consisting of lead oxide,lead sulfate and basic lead sulfate which comprises leaching the saidmaterial at a temperature in the range 15 to 35 C. and for a period notexceeding 1 hour with a mixture of ammonium sulfate and aqueous ammoniato produce a supersaturated solution having a composition within therange total sulfate 200 to 370 g./l., total ammonia 125 to 225 g./l. andtotal lead 10 to 140 g./l., separating undissolved substances, treatingthe resulting solution at a tempera ture in the range 45 to 65 C., inthe presence of 0. 1-400 g./l. of seed crystals of a salt selected fromthe group consisting of lead ammonium sulfate and basic lead sulfate,for a period of between 0.5 hour and 2.0 hours without substantial lossof ammonia to cause precipitation of a major portion of the lead thereinas a member of the group consisting of lead ammonium sulfate, monobasiclead sulfate and mixtures of these two compounds, separating theprecipitated solids and recycling the liquor to the leaching stage.

2. A process for the recovery of lead values from a material containing at least one compound selected from the group consisting of lead oxide, lead sulfate and basic lead sulfate which comprises leaching the said material at a temperature in the range 15* to 35* C. and for a period not exceeding 1 hour with a mixture of ammonium sulfate and aqueous ammonia to produce a supersaturated solution having a composition within the range total sulfate 200 to 370 g./l., total ammonia 125 to 225 g./l. and total lead 10 to 140 g./l., separating undissolved substances, treating the resulting solution at a temperature in the range 45* to 65* C., in the presence of 0.1-40.0 g./l. of seed crystals of a salt selected from the group consisting of lead ammonium sulfate and basic lead sulfate, for a period of between 0.5 hour and 2.0 hours without substantial loss of ammonia to cause precipitation of a major portion of the lead therein as a member of the group consisting of lead ammonium sulfate, monobasic lead sulfate and mixtures of these two compounds, separating the precipitated solids and recycling the liquor to the leaching stage. 